A method of adding conductive powder to a plastic, which is an example of a non-conductive material, is known as a method of providing conductivity to a plastic. Metal powder, carbon black, tin oxide doped with antimony or the like, and the like are known as examples of the conductive powder. However, the color of a plastic to which metal powder or carbon black has been added is black, and thus the application of the plastic may be restricted. On the other hand, the color of a plastic to which tin oxide doped with antimony or the like has been added is bluish black, and thus the application of the plastic may also be restricted as in the case where carbon black or the like is added. In addition, the issue of an environmental load arises due to the use of antimony. To address this, extensive studies on tin oxide in which an element such as antimony that incurs a large environmental load is not used as a dopant have been conducted.
Accordingly, tin oxide in which a halogen such as fluorine, which incurs a relatively small environmental load, is used as a dopant element has been proposed (see Patent Literature 1 to 3). Specifically, Patent Literature 1 states that tin oxide powder is brought into contact with 10 to 40 vol % fluorine gas in an inert gas atmosphere, and thus the tin oxide is doped with fluorine and imparted with conductivity. Patent Literature 2 describes transparent tin oxide powder that does not contain antimony, phosphorus, or indium, but contains fluorine in an amount of 0.3 to 5.0%. This transparent tin oxide powder is produced by adding fluorine or a fluorine compound to an aqueous solution of tin hydroxide and performing dehydration, followed by thermal treatment at 350 to 800° C. at a humidity of 50% or higher in an inert atmosphere. Patent Literature 3 describes a technique for cleaning conductive flooring with a composition containing a conductive pigment made of tin oxide doped with fluorine.
In addition to the above-described method, a method of performing hydrothermal treatment using an alkali suspension on tin hydroxide powder and then calcining the powder is also proposed as a method of producing tin oxide particles (see Patent Literature 4). Patent Literature 4 states that it is preferable to perform hydrothermal treatment under conditions in which the pressure is 2 to 150 kgf/cm2 and the temperature is 80 to 300° C.